A personal computer conventionally comprises a plurality of separate elements, which perform input, output and processing functions. In a desktop personal computer, these comprise for example the processor unit, a visual display unit (VDU) a keyboard, mouse and any other manual input devices as desired, and any other separate elements or peripherals to provide additional functions as required, for example speakers, printers etc. Conventionally, such elements are connected by appropriate cables. Such connections are however disadvantageous in that each cable requires at least one mechanical coupling or linkage which may be prone to wear or damage, the position of each element is naturally limited by the length of its associated cable, and, where a large number of elements or peripherals are provided, the resulting bundle of cables may be complex and unsightly.
The use of optical fibres to permit the transmission of signals in the form of modulated light levels or light pulses is well known. In U.S. Pat. No. 4,418,278, an input/output device is disclosed in which a page is provided with embedded optical fibres which are used either to transmit light from a suitable emitter to the surface of the page, or to receive light from the surface of the page and transmit the light to a suitable detector. In U.S. Pat. No. 4,418,278, a simple position indicating device is shown comprising a light pen. In a first alternative, the light pen comprises a light detector, and light is transmitted through each of the embedded fibres in turn. The timing of an optical pulse is detected by the pen indicates the pen position on the page. In an alternative, the pen comprises a light emitter. Light emitted by the pen is coupled into one of the fibres and detected by the detector corresponding to that fibre. Since the position of the fibre end is known, the position of the light pen is therefore also known. Such a system however only permits the use of a single, relatively simple pointing device.
An aim of the invention is to provide a new or improved communication device for a computer.